In recent years, the market of portable information devices such as cellular phones and electronic mail terminals has been rapidly expanding. With downsizing and lightening of these devices, their power supplies are also required to be downsized and lightened. Currently, lithium ion secondary batteries, which have a high energy density, are frequently used, but batteries with which a higher capacity is obtained are desired.
Air batteries using oxygen in the air for a positive electrode active material can be expected to have an increased capacity because it is not necessary to include a positive electrode active material in the battery. Particularly, nonaqueous electrolyte air batteries using lithium for a negative electrode have a high theoretical energy density and are being extensively studies.